The demands for sterilization has been increasing in daily life as well as in industrial, agricultural and food fields, and a variety of organic or inorganic antimicrobial agents are now in use.
Most of the conventional antimicrobial agents are synthetic ones with not a little toxicity. Recently, there has been progress in research in pursuit of reducing in toxicity, and development of polymer type fixed antimicrobial agents. The polymer type fixed antimicrobial agents are capable of imparting bactericidal activity to the surface of various objects and find broad application, for example, on the surface of fibers to provide antimicrobial and deodorizing fibers. Polymer type fixed antimicrobial agents heretofore reported include those comprising polymer chains, such as a vinyl polymer, polyacrylates, polymethacrylates, polyesters or polyamides, to which an antimicrobial agent is fixed as a pendant group. For example, an alkylpyridinium salt or an alkyldimethylbenzylammonium salt can be fixed to a vinyl polymer chain; a biguanide compound to a polyacrylate or polymethacrylate chain; and an alkylpyridinium salt to a polyester or polyamide chain.
Most of the reported fixed antimicrobial agents that have been put to practical use or under study are of the quaternary ammonium salt type. Although quaternary ammonium salt type fixed antimicrobial agents exhibit broad antimicrobial spectra, their antimicrobial effects produced through short time contact are insufficient.
Phosphonium salt type fixed antimicrobial agents so far proposed include polyvinylbenzylphosphonium salts as disclosed in WO92/14865.
Certain phosphonium salt compounds are known as a biologically active substance for their broad active spectra on bacteria, fungi, and algae similarly to various nitrogen-containing compounds (see Japanese Patent Laid-Open Nos. 57-204286, 63-60903, 1-93596, 2-240090, and 62-114903). However, the antimicrobial activities of these phosphonium salt type antimicrobial agents are insufficient similar to the quaternary ammonium salt type.
Japanese Patent Laid-Open No. 4-266912 discloses an antimicrobial polymer which exhibits sufficient antimicrobial effect through short time contact as well as a broad antimicrobial spectrum. However, since the monomer essential to the polymer has a low rate of polymerization, which is allowable when the monomer is homopolymerized, it is difficult to copolymerize with other monomers having greatly different polymerization rates. Further, that monomer has insufficient hydrophilic properties and, in particular, with its alkyl chain greatly extended, has poor compatibility to hydrophilic comonomers. Furthermore, the copolymers have low activities.
On the other hand, contact lenses in general use, either hard or soft, are apt to be contaminated with bacteria and fungi as microorganisms easily grow between the contact lens and the cornea with adequate moisture, temperature and nutrients.
Hard contact lenses tend to mechanically damage the cornea, causing infection with microorganisms. Those for continuous wear, which have recently been increasing are particularly dangerous. Further, bacteria, fungi, etc. may grow on the surface of hard contact lenses in a lens container, sometimes causing corneal infectious diseases.
Water-containing soft contact lenses, while comfortable to apply, are susceptible to bacteria and fungi both on the surfaces and in the inside thereof because of their own hydrophilic properties as well as their high water content, tending to cause serious infectious diseases. Moreover, they demand care in handling and involve tedious treatment for sterilization.
Under these circumstances, studies and development of contact lenses endowed with antimicrobial properties have been promoted. For example, a contact lens comprising a chitosan derivative as a matrix and a contact lens having a resin coat containing a chitosan derivative have been proposed (see Japanese Patent Laid-Open Nos. 63-217319 and 3-102313, respectively). However, the antimicrobial contact lenses proposed are unsatisfactory in optical performance and duration of antimicrobial action.
Bacteria and fungi also propagate in contact lens-care articles, such as containers, to cause secondary infection. Therefore, it has been proposed to add an antimicrobial agent to the lens soaking solution, lens cleaner, and the like, thereby to suppress propagation of microorganisms.
However, use of a large quantity of an antimicrobial agent or a potent antimicrobial agent is unfavorable to the lens and the body, especially the cornea. Hence, means for controlling microorganisms without addition of an antimicrobial agent have been studied. Resins coated with an antimicrobial substance have been proposed, but they are unsuitable for use as contact lens-care articles because of considerable elution of the antimicrobial substance during use.
Where antimicrobial properties are imparted to a contact lens per se, special care for safety is required; for a contact lens comes into direct contact with the cornea and the conjunctiva, and any substance eluted from the lens is carried by tears to the digestive tract. Accordingly, an antimicrobial substance to be incorporated into contact lenses and related articles is essentially required to have high activity and heat stability and to be firmly fixed so as not to be dissolved out. From these considerations, phosphonium salt type polymers are deemed to be suitable.
Where an antimicrobial phosphonium type polymer is applied to contact lenses, it should be noted that the lens must exert the antimicrobial activity while retaining other properties essential to contact lenses, such as optical performance (i.e., transparency, uniformity, and heat stability), processability, strength, safety, and the like.
An object of the present invention is to solve the above-mentioned problems, and provide a novel phosphonium salt-containing polymer.
Another object of the present invention is to provide an antimicrobial agent comprising the phosphonium salt type polymer as an active ingredient, which has a broad antimicrobial spectrum and produces sufficient antimicrobial effect in a short period of contact.
A further object of the present invention is to provide a contact lens and contact lens-care articles which are substantially free from contamination by bacteria, fungi, etc. and from which the antimicrobial substance barely dissolves out.